The present disclosure relates generally to the field of ophthalmics, more particularly to ophthalmic devices, including intraocular lenses (IOLs) such as accommodating intraocular lenses.
A healthy young human eye can focus an object in far or near distance, as required. The capability of the eye to change back and forth from near vision to far vision is called accommodation. With reference to FIG. 1A, accommodation occurs when the ciliary muscle CM contracts to thereby release the resting zonular tension on the equatorial region of the capsular bag. The release of zonular tension allows the inherent elasticity of the lens capsule to alter to a more globular or spherical shape, with increased surface curvatures of both the anterior and posterior lenticular surfaces.
In addition, the human lens can be afflicted with one or more disorders that degrade its functioning in the vision system. A common lens disorder is a cataract which consists of the opacification of the normally clear, natural crystalline lens matrix. The opacification can result from the aging process but can also be caused by heredity or diabetes. FIG. 1A shows a lens capsule comprising a capsular sac with an opacified crystalline lens nucleus. In a cataract procedure, the patient's opaque crystalline lens is replaced with a clear lens implant or IOL.
In conventional extracapsular cataract surgery as depicted in FIGS. 1B and 1C, the crystalline lens matrix is removed leaving intact the thin walls of the anterior and posterior capsules—together with zonular ligament connections to the ciliary body and ciliary muscles. The crystalline lens core is removed by phacoemulsification through a curvilinear capsularhexis as illustrated in FIG. 1B, i.e., the removal of an anterior portion of the capsular sac. FIG. 1B depicts a conventional 3-piece IOL just after implantation in the capsular sac.
FIG. 1C next illustrates the capsular sac and a conventional 3-piece IOL after a healing period of a few days to weeks. The capsular sac effectively shrink-wraps around the IOL due to the capsularhexis, the collapse of the walls of the sac and subsequent fibrosis. With reference to FIGS. 1B and 1C, cataract surgery as practiced today causes the irretrievable loss of most of the eye's natural structures that provide accommodation. The crystalline lens matrix is completely lost—and the integrity of the capsular sac is reduced by the capsularhexis. The “shrink-wrap” of the capsular sac around the IOL can damage the zonule complex, and thereafter it the ciliary muscles may atrophy. Thus, conventional IOL's, even those that profess to be accommodative, may be unable to provide sufficient axial lens spatial displacement along the optical axis or lens shape change to provide an adequate amount of accommodation for near vision.
Accommodative Lens Devices
Several attempts have been made to make intraocular lenses that provide the ability to accommodate. Such attempts generally fall into two categories: those that rely on changing the shape of optical elements, and those that rely on changing the relative position of one or more optical elements. In the second category, changes in power are brought about by making the intraocular lens or a lens component move back and forth (anterior and posterior) along the optical axis. Such displacements change the overall optical power of the eye and may allow a patient to adjust his or her focus so as to create sharp retinal images of objects over a range of distances. Examples of such attempts are set forth in Levy U.S. Pat. No. 4,409,691 and several patents to Cumming, including U.S. Pat. Nos. 5,674,282; 5,496,366; 6,197,059; 6,322,589; 6,342,073; and 6,387,126.
Specially shaped haptics, levers or other mechanical elements have been described to translate the radial compressive force exerted by the zonules to the desired axial displacement of a lens body, including in U.S. Pat. Nos. 7,018,409; 6,790,232; 6,524,340; 6,406,494; and 6,176,878. These haptics are often fused to the capsular wall by the fibrosis occurring during the post-operative healing phase. Additional examples may also provide flexible hinge regions of the haptic to facilitate axial displacement, including U.S. Pat. Nos. 5,496,366; 6,969,403; 6,387,126 and 7,025,783. Several examples include annular rings elements to facilitate contact with the capsule and translation of the compressive application of force by the zonules to effect axial displacement of the lens body, including in U.S. Pat. Nos. 6,972,033 and 6,797,004; and U.S. Publication No. 2004/0127984. However, many of these IOL's are configured to be generally planar, and parallel to the plane of the lens, thus minimizing the natural spheroid shape of the capsular bag and reducing the natural accommodative ability of the eye. The disclosure of each of the aforementioned patents is incorporated herein by reference.
In most of the aforementioned embodiments, the lenses are biased to be located in the posterior-most position in the eye under rest or resting conditions. When near focus is desired, the ciliary muscle contracts and the lens moves forwardly (positive accommodation). In the absence of ciliary muscle contraction, the lens moves rearwardly to its posterior-most resting position. One problem that exists with such IOLs is that they often cannot move sufficiently to obtain the desired accommodation.
Accommodative lens designs with single or multiple optic lens assembly have been disclosed in U.S. Pat. Nos. 6,423,094; 5,275,623; 6,231,603; 4,994,082; 6,797,004; 6,551,354; and 6,818,017. In these designs, the optic diopter of an individual lens does not change during the accommodation-unaccommodation process. Rather, the optic diopter power of the assembly is dependent on the distance between the optic lenses. These designs also incorporate a framework that flexes about a generally equatorial plane, orthogonal to the optical axis, to affect movement of the lens bodies at one or both distal framework ends along the optical axis. However, multiple lens systems can be cumbersome and also require an axial displacement unachievable with a collapsed capsular bag and resulting ineffective accommodative mechanisms. Furthermore, IOL's of this configuration flex about a plane parallel to the plane of the lens body, translating the compressive action of the accommodative mechanisms into axial displacement along the optical axis. Thus the accommodative effect is to axially displace the optics along the optical axis, not provide compressive force radially inward orthogonal to the optical axis.
On the other hand, lens surface shape changing, exemplified in the disclosures of U.S. Pat. Nos. 4,842,601; 4,888,012; 4,932,966; 4,994,082; 5,489,302; 6,966,049; and U.S. Publication Nos. 2003/0109926; 2003/00639894; 20050021139A1; and 2005/1890576 have required a spherical lens shape to interact with the rim of ciliary muscle in more than one meridian or even from all 360 degree orientations. This requires perfect lens centration in regard to the ciliary rim and equal interaction from all meridians; otherwise, the absence of central lens symmetry leads to unequal lens surface curvature in different meridians with resulting reduction in image quality.